ETS Plugin - 'A security error occurred' when using programatically

hi,

I get  "A security error occurred" error when I try to run a Pre-translate task programatically via the Studio API, using the ETS plugin as translation provider.

I add the cretentials for the provider (ets://server:8001) in this format: "user=xxxx;password=yyyy", then run the pre-translate task like this:

sdlProject.RunAutomaticTasks(projectFiles.ToArray(), taskTemplateIds);

If I run a request like this from the same console application, it works properly:

using (HttpClient httpClient = new HttpClient())
{
  var uri = new Uri("https://server:8001/api/v2/auth?username=xxxx&password=yyyy");
  HttpResponseMessage result = httpClient.PostAsync(uri, (HttpContent)null).Result;
}

But the same request with exactly the same uri fails inside ETSTranslatorHelper.GetAuthToken(), when I start the pretranslation task programatically. 

When using the plugin from Studio itself, it works properly. The authentication request above also succeeds (I put a breakpoint there).

Do you have an idea what setting may be missing, or what do I wrong?

Thanks,

Tamas